1. Field of the Invention
The field of the invention pertains to electrostatic, hand-held, spray guns.
2. The Prior Art
Electrostatic spray guns are known from the prior art in which a high voltage generator is located in a cabinet at a distance from the gun. A high voltage cable, up to several meters long, connects the pistol body with the high voltage generator. This high voltage cable has several well recognized disadvantages due to the fact that the cable must of necessity be heavy and thick in order to properly insulate the high voltages, on the order of 70 to 90 kv, from the surrounding environment.
It has also been known in the prior art to incorporate the high voltage generation electronics in the pistol itself. In the prior art spray guns, the high voltage generating electronics, comprising usually a voltage multiplier formed of diodes and capacitors having an elongated shape, has either been located adjacent and coextensive to a boring through the pistol barrel through which the color material passes or, alternately, has been located so that it surrounds the boring through the barrel. It has also been recognized in the prior art that the high voltage multiplier section must be encapsulated in an appropriate potting compound for insulation purposes. Thus, the prior art pistols have been constructed with a barrel wherein the high voltage multiplier section has become permanently bonded thereto and an integral part thereof.
Typical prior art guns, wherein the high voltage diode capacitor multiplier electronics has been mounted in the gun, are disclosed in:
U.S. Pat. No. 3,599,038 to Skidmore, PA1 U.S. Pat. No. 3,731,145 to Senay, PA1 U.S. Pat. No. 3,608,823 to Buschor.
While the practice of encapsulating the high voltage generator system in the barrel of the pistol has advantages from the standpoint of the weight of the pistol and the costs of manufacture of it, there are also disadvantages which have been recognized which are inherent to this structure. One disadvantage is that with the high voltage generator system being an integral part of the barrel, it is impossible to repair a defect in the high voltage system. Thus, unless the barrel has been designed to be removable, the entire pistol must be replaced if the high voltage generator system fails.
If for some reason there is a failure in the color distribution system through the handle and barrel through which the color material passes, at the very least, once again the barrel structure including the high voltage generator system must be replaced. Further difficulties are encountered where it is desirable to house a number of color borings in the pistol barrel so that the gun might apply more than one color readily.
Additionally, it has been found that where the high voltage generator system has been located so as to be longitudinally adjacent to or to surround the boring through the barrel that difficulties occur in hot spraying. The heat transfer from the color boring through the voltage multiplier which due to the well known temperature dependency of semiconductors, degrades the performance of the high voltage multiplier structure.
Thus, there has been a need for a hand-held spray pistol with a high voltage generator system mounted in the pistol so that the generator system may be easily serviced or repaired, and may also be used with hot spraying techniques.